The increase in the amount of traffic resulting from the rising number of communications subscribers, as well as more stringent requirements for the amount of data to be transmitted, means that switching devices, such as private branch exchanges, are subject to ever more stringent requirements. For example, the amount of data to be transmitted per communications link, and the number of communications terminals which can be connected to one another. Present-day devices are based, for example, on the TDM method (Time Division Multiplexing) in which communication data relating to different connections is transmitted in respectively defined time slots. Connection between different communications partners is produced by a switching matrix, which allocates incoming time slots on an incoming connection to outgoing time slots on an outgoing connection, on the basis of control information. Switching matrices such as these are generally of a fixed size and can produce only a defined number of connections, which often makes it harder to adapt switching systems to meet the requirements. Devices such as these have a further problem in that the time slots can hold a limited amount of data. For example, a switching matrix can produce 4096 connections, while a maximum of 64 KBits of data can be transmitted within one time slot. An increasing number of subscribers can thus only ever be coped with in groups of 4096 connections. However, utilization of these different extension levels demands additional development effort to match the switching device to the greater number of subscribers. It is likewise impossible without problems to increase the amount of communication on each connection in a flexible manner, and this can best be done by setting up two or more communications links, e.g. in the form of a 64 kbit fit. In practice, this type of bandwidth duplication has, however, not been implemented for ISDN (Integrated Services Digital Network) transmission, and scarcely any terminals are available for this purpose.